Various blood processing systems now make it possible to collect particular blood constituents, rather than whole blood, from donors or patients. Typically, in such systems, whole blood is drawn from a donor, the particular blood component or constituent is removed and collected, and the remaining blood constituents are returned to the donor. By thus removing only particular constituents, potentially less time is needed for the donor's body to return to pre-donation levels, and donations can be made at more frequent intervals than when whole blood is collected. This increases the overall supply of blood constituents, such as plasma and platelets, made available for health care.
Whole blood is typically separated into its constituents through centrifugation. This requires that the whole blood be passed through a centrifuge after it is withdrawn from, and before it is returned to, the donor. To avoid contamination and possible infection of the donor, the blood is preferably contained within a sealed, sterile fluid flow system during the entire centrifugation process. Typical blood processing systems thus include a permanent, reusable centrifuge assembly containing the hardware (drive system, pumps, valve actuators, programmable controller, and the like) that spins and pumps the blood, and a disposable, sealed and sterile fluid circuit that is mounted in cooperation on the hardware. The centrifuge assembly engages and spins a separation chamber of the disposable fluid circuit during a blood separation step. The blood, however, makes actual contact only with the fluid circuit, which assembly is used only once and then discarded.
As the whole blood is spun by the centrifuge, the heavier (greater specific gravity) components, such as red blood cells, move radially outwardly away from the center of rotation toward the outer or “high-G” wall of the separation chamber of the fluid circuit. The lighter (lower specific gravity) components, such as plasma, migrate toward the inner or “low-G” wall of the separation chamber. Various ones of these components can be selectively removed from the whole blood by forming appropriately located channeling seals and outlet ports in the separation chamber of the fluid circuit. For example, one application of therapeutic plasma exchange involves separating plasma from cellular blood components, collecting the plasma, and returning the cellular blood components and a replacement fluid to the donor.
After the blood has been separated into its constituent parts, it may be desirable to further process one more of the separated components. For example, in an alternative version of a therapeutic plasma exchange procedure, rather than replacing a patient's plasma with a different fluid, the patient's own plasma may be treated and returned after separation. This may be most efficiently achieved by pairing the blood separation system with a secondary processing device, such as an adsorption device or column. The adsorption device will remove undesirable substances from the plasma by immuno-adsorption. The exact substances removed depend upon the needs of the patient. For example, the substances removed from the plasma by the adsorption device may include low-density lipoproteins and Lipoprotein(a) for patients suffering from severe hypercholesterolemia. In another example, pathogenic antibodies may be removed from the plasma, for patients suffering from autoimmune diseases and organ transplant rejection, or as a pre-treatment before transplantation. In yet another example, fibrinogen, fibrin, and/or C-reactive protein may be removed from the plasma, for treating microcirculation disorders and ischemic tissue damage. Exemplary adsorption devices include the TheraSorb® line of products from Miltenyi Biotec GmbH Corporation of Bergisch Gladbach, Germany. Other examples of adsorption devices suitable for removing undesirable substances from plasma are described in greater detail in U.S. Pat. No. 6,569,112 to Strahilevitz, which is incorporated herein by reference.
One disadvantage of known centrifugation systems, particularly when used in therapeutic plasma exchange procedures, is that separated plasma in the centrifuge may flow into a return line for cellular blood components, rather than flowing into the plasma collection line. Such plasma in the wrong line will fail to be treated prior to return to the patient, meaning that the efficiency of the system is not only diminished, but there is a corresponding effect on the health benefits experienced by the patient. Another disadvantage of known centrifugation systems is that cellular blood components may flow into the plasma collection line, rather than flowing to the patient via a return line. Cellular blood components, such as platelets, in the separated plasma may have a negative effect on the health of the patient. Accordingly, the need remains for a centrifugation system with additional safety features and improved plasma collection efficiency with low cellular loss.